Plants processing foods, pharmaceuticals, biological and technological fluid materials generally require fluid piping systems that must be free from voids and crevices to prevent accumulations of materials, that can readily be taken apart for periodic cleaning and that can withstand the application of CIP (clean in place) solutions and steam cycles used for cleaning. The gasket material used at joints in the piping systems must have appropriate resiliency and resistance against deterioration by the chemical and physical characteristics of the fluids under the conditions of temperature and pressure occurring during santization, such as the use of 15 psi saturated steam, hot, de-ionized water or hot WFI (water for injection). One early form of sanitary coupling, shown in U.S. Pat. No. 2,985,470, employed a conical gasket machined from polymeric tetrafluoroethelene that provided a pair of parallel, conical surfaces with cylindrical inner and outer surfaces. More recently, assembly and disassembly of pipe sections has been facilitated by using flanged pipe ends held together by hinged clamps rather than by threaded coupling, such as shown in U.S. Pat. No. 4,568,115. The flanged pipe ends may be sealed against leakage through the use of O-ring gaskets, such as shown in U.S. Pat. Nos. 5,904,382 and 5,971,399.
The '382 patent noted that the gasket shown in the '470 patent was subject to being objectionably deformed when clamped between opposed ends of the pipes of a pipe fitting so that it became unusable after several uses. In an attempt to make the gasket re-usable, the '399 patent resorted to a gasket made of porous, composite materials having different densities and which were differently compressible, so as to offer both effective sealing as well as resistance to cold flow.
In the light of the requirements set forth in a 1995 report prepared by the Subgroup Pipe Couplings of the European Hygienic Equipment Design Group entitled “Hygienic Couplings”, dealing with joint sealing against contamination by microorganisms, each of these prior art approaches may be seen to have some short-comings. Among the points made in the report is that, to provide a bacteria-tight seal, valleys in the surface profile of the coupling joint must be filled by the elastomeric gasket material, typically by tightening the fastening device holding the coupling together, until sufficient contact pressure is applied. If too little contact pressure is applied by the fastening device, valleys in the surface profile will not be adequately filled to prevent accumulation of micro-organisms and if too much pressure is applied the gasket material may be extruded into the pipe lumen thereby causing an obstruction or partial dam that could cause material to be trapped.
One approach to obtaining the desired degree of gasket compression is to use a torque wrench on the clamping screw of the clamp holding the pipe sections together. Another approach is disclosed in my U.S. Pat. No. 6,082,941, assigned to the assignee of the present invention in which the tightening of the coupling is controlled by a torque-limiting fastener.
While the foregoing approaches offer some protection against over-compression of the gasket material, it would be desirable to provide a gasket suitable for use with sanitary pipe couplings that itself prevented intrusions into the lumen of the sanitary piping.